1. Field of the Invention
This invention relates to a selector switch for an asynchronous network of concurrent processors and more particularly to such a switch which is adapted to be cleared when it is part of the node in the network that has become clogged by a message passing through the network.
2. Description of the Prior Art
Arbiter switches and selector switches are employed in the formation of networks for asynchronous transmission from one source node to one of a number of destinations in the network. An arbiter switch is a switch or node which receives such asynchronous transmission from one of two different input ports and transfers that message in an asynchronous manner to its output port. Such an arbiter switch is disclosed in detail in the Clark U.S. Pat. No. 4,251,879 which is assigned to the assignee of the present invention. A selector switch is a switch which receives a message on its input port and transmits it to one of two output ports according to the first bit in the serial transmission to be received. Such a selector switch is disclosed in the Clark U.S. Pat. No. 4,237,447 which is assigned to the assignee of the present invention. By employing these two switches, various networks of a variety of configurations can be created as is described in the Barton et al patent application Ser. No. 035,314, filed Feb. 2, 1979 and assigned to the assignee of the present invention.
In the implementation disclosed in the above described patents, when it is desired for one node to transmit a message to another node, it begins its transmission which establishes a path between respective nodes, which path becomes dedicated to that transmission until an end-of-message signal is received by the destination and an acknowledge end-of-message signal is transmitted back through the various switches of the network forming the path to the source. This causes a delay in freeing the network for the establishment of different transmission paths due to the time that it takes for the end-of-message signal to reach the destination and the acknowledge end-of-message signal to be transmitted back to the source. Of equal importance in a concurrent network, after a few paths have been established between different nodes, it becomes increasingly difficult for other sources in the network to establish a transmission path for transmission to one of the destinations. As a practical matter, the problems of tying up a goodly portion of the network are increased by the possibility of a malfunction of a component in one of the nodes or switches so that it does not react to the appropriate end-of-message acknowledgment signal.
In the above-described Clark patents, a particular node is cleared only by the reception of an acknowledgment end-of-message signal with the inherent problems that were discussed above. Therefore, it is advantageous to be able to have a network of such switches that may be "cleared" or reset whenever a transmitting processor determines that one or more switches in a particular transmission path are no longer operative.
It is, then, an object of the present invention to provide an improved selector switch for an asynchronous network of concurrent processors.
It is another object of the present invention to provide an improved selector switch for such an asynchronous network wherein a particular transmission path is not continuously dedicated for the duration of transmission of a particular message along the path.
It is still a further object of the present invention to provide an improved selector switch for such an asynchronous network which may be cleared or reset when it is determined that a particular path in the network is not operating properly.